Inclinometer



Dec. 26, 1 961 5. Wm 3,014,282

INCLINOMETER Filed Sept. 2, 1958 FREQUENCY FIG. 6

FIG. I v INVENTORZ EDWARD B. WIST This invention pertains to inclinometers and more particularly to an inclinometer which is used to indicate the deviation of a well bore from a vertical position.

In well drilling operations and particularly the drilling of oil wells, it is necessary to know the exact inclination of the borehole during the drilling operation. This inf formation is necessary in order to insure that the well as drilled is in the proper location and does not deviate or encroach upon other locations. Also, .in some instances particularly oifshore installations, wells are drilled at definite angles in order that a plurality of wells may be drilled from a single platform.

The problem of crooked or inclined boreholes'is particularly difiicult in some sectionsof the country where well bores tend to deviate from the vertical more easily than in most. In these sections of the country conservative drilling practices must be followed in order to prevent deviations of the well bore from thevertical. These conservative practices result in much slower drilling speeds and excessive interruptions in order to measure -the in-' clination of the borehole.

In the past, instruments have been developed which depend on a. pendulum for determining deviations of the boreholes from a vertical position. As is well known, a pendulum tends to assume a vertical position, thus, if a pendulum is mounted in a drill string and it tends to deviate or incline the pendulum will remain vertical and a suitable means can be provided for measuring the deviation. In these prior devices two general means were used for detecting the position of the pendulum. One of these methods utilized photographic plates or other sensitive material to record the position of the pendulum while the other method utilized a system for generating pressure pulses or surges in the drilling mud which were proportional to the inclination of the pendulum. The use of photographic material, of course, necessitates the removal of the inclination instrument from the well bore in order to develop the photograph. The use of pressure pulses or surges to detect the inclination of the pendulum eliminates the necessity for removing the inclinometer from the well bore but it does require a stopping of both the drill rig and circulation of the drilling mud when it is desired to take a reading. While the time required to take a reading with an instrument utilizing a pressure pulse method of measuring is only a few minutes it results in a considerable expenditure of money when the high cost of drilling rigs and their operation is considered. Also, the large number of readings required during the drilling of a deep well result in a considerable time delay and add to the cost of drilling. a

As can be appreciated both of the above methods are costly and not entirely satisfactory. Even though the problem has been apparent to those working in the field of'well drilling, no satisfactory solution has been proposed. In order to be entirely satisfactory an inclinometer should give accurate readings of the borehole inclination while the drilling rig is operating. Furthermore, the inclinometer should require a minimum of equipment, such as amplifiers and the like to be installed in the drill string for transmitting the signal to the surface. Of course, in any case, the inclinometer must be of rugged design so that it is not damaged during the normal course of drilling operations. 7

Accordingly, it is the principal object of this invention ted States Patent 3,014,282 Patented Dec. 26, 1961 to provide a novel inclinometer which will determine the inclination of a well bore and transmit a signal without requiring'removal of the instrument.

A further object of this invention is to provide a novel inclinometer which utilizes mechanical means to transmit its signal to the surface of the well and requires no electrical connections between the downhole instrument and the surface of the well.

A still further object of this invention is to provide an inclinometer which utilizes a vibrating member to determine the inclination of a well bore with the mass of the vibrating member being changed in response to the inclination of the drill string and, thus, its frequency of vibration also changes as a function of the inclination. V A further object of this invention is to provide an inclinometer utilizing a vibrating member whose frequency of vibration is related to the inclination of the drill string with the vibrations from the vibrating member being induced in the drill string and detected at the well head in order to obtain continuous indication of the inclination of the drill string.

The above objects and other advantages of this inven tion are accomplished by utilizing the principle that the frequency of vibrationot' any member having a fixed physical size varies inversely with the square root of the mass of the member. The invention utilizes two closed chambers, one fixed and one free to vibrate, with the chambers being connected together by an elastic member. lnaddition, means are provided for establishing fluid communication between the upper portions of both chambers and between the lower portions of both chambers. Thus, if the chambers are filled with two (or more) immiscible fluids having different specific gravities and mounted. so that these fluids have free access through the fluid com munication means to both chambers the mass of the members will vary with the inclination of the device. The vibrating member is located so that the flow of drilling mud impinges thereon to maintain it in a vibrating state While the fixed member is securely attached to the drill string so that the drill string may be utilized to transmit the vibrations of the vibrating member to the well head where they may be detected by suitable means, such as a microphone or the like. The detecting system, of course, will detect all vibrations in the drill string but the random vibrations may be readily filtered out so that only the vibrations due to the inclinometer remain. The variation in the frequency of the vibrations from the inclinometer are an indication of the inclination of the drill string. a

.The above objects and advantages of this invention will be more easily understood by those skilled in the art from the following detailed descriptionof a preferred embodiment when taken in conjunction with the enclosed drawing: V

FIGURE 1 shows the inclinometer of this invention mounted adjacent the lower end of the drill string and a circuit used for detecting the vibrations induced in the drill string by the inclinometer;

FIGURE 2 is an enlarged horizontal section taken along line 22 of FIGURE 1 and showing a top view of the inclinometer;

FIGURE 3 is a vertical section taken along line 33 of FIGURE 2 and showing a vertical section of the inclinometer;

FIGURE 4 is'another vertical section taken along line 4-4 of FIGURE 2 and showing an end view of the .in-

clinometer;

nometer in an inclined position.

FIGURE 5 is a schematic representation of the inclinometer in a vertical position, and I FIGURE 6 is a schematic represntation of the incli- Before describing the inclinometer of this invention in detail the physical laws which govern its operation should be reviewed. It is well known that a member of fixed physical size when disposed in a flowing stream will vibrate at a fixed frequency with amplitude of the vibration depending on the velocity of the stream. It is also Well known that if the mass of the member is changed without changing its elastic characteristics its frequency of vibration will decrease with an increase in the mass of the member and will increase as the mass of the member decreases. Thus, if a device can be provided whose mass will vary with the inclination of the drill string and a means provided for maintaining it in the vibratory state a suitable inclinometer can be devised. In order to overcome the difficulties which arose in prior devices in transmitting the signal from the inclinometer to the surace of the well this invention utilizes the drill string itself as a means for transmitting the signal. This is possible with the inclinometer of this invention since the signal from the inclinometer is in the form of vibratory motion which motion may be easily induced in the drill string and detected at the surface of the well. Of course, the vibratory motion could also be induced in other media, for example the drilling mud used in drilling the Well.

Referring now to FIGURE 1, the-re is shown a tubular drill string with a drill bit 11 attached to its lower end. The inclinometer 12 of this invention is securely fastened to the drill string adjacent its lower end to insure that the vibration of the inclinometer will be induced in the drill string 10. While the inclinometer is shown as being mounted on the internal surface of the drill string it could also be mounted on the external surface of the drill string or other locations on the drill string. In some installations the normal flow of drilling mud being circulated through the drill string may be insuificient to maintain the inclinometer vibrating. In these cases it will be necessary to restrict the interior of the drill string to increase the velocity of the mud stream as it flows by the inclinometer. The instrument is completed by means of a detector circuit 15 which is mounted at the well head and used to detect the vibrations induced in the drill string 10 by the inclinometer.

While a flow directing passage may be necessary for increasing the velocity of the drilling mud stream impinging on the vibrating portion of the inclinometer in many cases such an arrangement will be unnecessary since the drilling mud stream itself will have suflicient velocity. In some cases the motion of the drilling rig will also be suflicient to maintain the vibratory state of the inclinometer. Also, while the inclinometer is shown as being mounted directly on the tubing which forms the drill string it could easily be made as a separate unit and installed near the lower end of the drill string between two joints thereof.

Reference is now made to FIGURES 2, 3, and 4 which show the actual construction details of the inclinometer 12. The inclinometer utilizes a first closed chamber which is connected to a second closed chamber 21 by means of an upper elastic or flexible tube 22 and a lower elastic or flexible tube 23. The closed chamber 21 is provided with slanting side walls 27 as shown in FIGURE 4 in order that its cross-section as seen in FIGURE 4 will approach a semicircular shape. While a member of any given cross-section will vibrate when disposed in a fluid flow, the amplitude of the vibration varies considerably with various cross-sections with the same flow impinging on each section. A streamline shape will produce the smallest amplitude of vibration while a semicircular shape with the flow impinging on the flat surface will produce the largest amplitude of vibration with the same flow impinging on both shapes. A flat plate will also produce a large amplitude vibration if it is disposed so that the flow is perpendicular to its flat surface. Since the closed chamber 21 forms the vibrating member of the inclinometer, the material used for forming the tubes 22 and 23 should have sufiicient elasticity to permit vibration of the chamber 21 while retaining the chamber 21 in its proper position. A suitable material for the tubes 22 and 23 would be hard brass or stainless steel.

While a preferred arrangement for joining the vibrating chamber 21 to the fixed or reservoir chamber 20 is the two elastic tubes 22 and 23 described above. other arrangements may be used. One such arrangement would be to secure the chambers 20 and 21 together by a solid elastic web and use separate flexible tubes to provide communication between the upper portions of the chambers and the lower portions of chambers. Another method would be to form fluid communication passages directly in the elastic Web.

The closed chamber 20 may be formed from a closed end tube 24 which is closed at its upper end by means of a threaded cap 25. The tube ing plate 26 by any desired means such as welding or the like with the mounting plate 26 in turn being secured to a web 30 by means of machine screws 31. The web 30 is securely fastened to the interior surface of the drill string 10 by means of welding or the like. It should be noted that the inclinometer is mounted so that the vertical axis of the closed tubular member 20 is disposed in a parallel relationship to the vertical axis of the drill string 10. The inclinometer instrument is completed by filling the interior of the closed tubular member 20 and the closed chamber 21 with two immiscible fluids 32 and 33 having different specific gravities. Two suitable fluids would be mercury and a light oil, although many combinations of fluids having different specific gravities may be used. While two fluids are preferred a greater number could also be used if it was desired and the inclinometer would still operate satisfactorily.

Referring again to FIGURE 1, there is shown a circuit 15 for detecting the vibrations induced in the drill string 10 by the inclinometer. The detecting means consists of a microphone 40 which is physically connected to the drill string 10 by means of a connection shown schematically at 41. Thus, the vibrations in the drill string will generate a fluctuating electric signal in the microphone 40 which may be amplified by an amplifier 42. The amplified signal is then passed through a suitable filter circuit 43 in order to remove all of the frequencies except those which correspond to the vibrations induced in the drill string by the inclinometer. Finally, the filtered fluctuating electric signal is passed through a frequency meter 44 where the actual variation in the frequency of the signal may be determined and any variation of frequency of the signal will of course indicate any inclining of the inclinometer and in turn the portion of the drill string 10 to which the inclinometer is attached.

Referring to FIGURES 5 and 6, there is shown a schematic arrangement of the closed tubular member 20 and the closed chamber 21. FIGURE 5 shows the inclinometer in a vertical position in which case the interface between the two fluids 32 and 33 will be at approximately the center of the instrument. FIGURE 6 shows the axis of the inclinometer inclined at an angle theta from the vertical. It can be seen in this figure that the mass of the closed chamber 21 has been greatly increased due to the greater quantity of the fluid 32 contained therein. This increase in the mass of the closed chamber 21 will reduce the frequency of its vibrations. This reduction in the frequency of vibrations will be indicated by the frequency meter 44 of the detector circuit and, thus, by proper calibration the inclinometer may be used to measure the inclination of various well bores.

When the inclinometer described above is installed adjacent to the lower end of the drill string it must be securely installed in order that the vibrations of the inclinometer will induce similar vibrations in the drill string and, accordingly, it is preferable to weld the web 30 directly to the drill string 10. This will insure that the maximum amount of the vibration induced in the 24 is secured to a mountchamber 21 by the impinging mud stream is transferred to the drill string for transmission to the surface. The frequency of these vibrations will vary as the axis of the inclinometer is moved from a vertical position. If the drill string is inclined from the vertical and rotated at the same time the inclinometer will generate a vibration whose frequency will vary between a maximum and minimum value as the mass of the closed chamber 21 varies betwen two limits during a complete rotation of the drill string. Thus, it can be seen that the vibrations of the inclinometer will indicate the deviation of the drill string from the vertical position.

The circuit 1'5 will indicate the change in the frequency of the vibrations between the two limits and it is necessary to calibrate the inclinometer in order to convert these frequencies into actual inclination'readings. Any particular instrument will emit a characteristic fixed frequency of vibration when disposed in a vertical position and its frequency of vibration will vary over a characteristic range of frequencies if the drill string is rotated in an inclined position.

Instead of using the drill string to transmit the vibrations of the closed chamber 21 to the surface other means may be used. For example, the vibrations could be converted to an electrical signal which would be transmitted to the surface over a circuit utilizing the drill string as a conductor. Also, other systems could be used such as used with previous inclinometers. Of course, while they could be used these previous systems would all have the disadvantages pointed out above.

While the inclinometer described above can be operated under most conditions with the'drill string rotating at its normal speed in some cases it may be necessary to slow the drill string or stop it completely. When the drill string is stopped it will be necessary to raise it slightly and then start it rotating in order to take a reading since, as explained above, it is necessary to rotate the drill string in order to obtainv a reading which will vary between a maximum and minimum frequency. This will be particularly true in cases where the drill rig itself generates vibrations within the same frequency band as the inclinometer. While it may be necessary to stop and raise the drilling rig it will be a stop of short duration and will not materially effect the operation of the rig. In addition, in cases where the drill string is used to transmit the vibrations to the surface no additional equipment is required and no leads or other connections through the drill string are required. This greatly simplifies the running of the drill string since it is not necessary to pass a conductor cable through each section of the string or make connections between the various sections in order to transmit an electrical signal from the downhole instrument to the surface.

Accordingly, while only one embodiment .of this invention has been described in detail, many modifications and improvements will, occur to those skilled in the art to which it pertains within its broad spirit and scope.

I claim as my invention:

1. An inclinometer for drill strings comprising: an enclosed reservoir chamber; a hollow vibrating chamber;

an elastic member for connecting said reservoir and said vibrating chambers together, first conduit means providing communication between the upper portions of said chambers and second conduit means providing communication between the lower portion of said chambers, said reservoir and said vibrating chambers being filled with at least two immiscible fluids having different specific gravities; said reservoir chamber being securely fastened to the drill string adjacent the drill bit and disposed to permit said vibrating chamber to vibrate; means including the drilling fluid for causing said vibrating chamber to vibrate; and means for determining the frequency of vibration of said hollow member.

3. An inclinometer for drill strings comprising: an enclosed reservoir chamber; a hollow vibrating member, an elastic member for connecting said reservoir and said vibrating chambers together, first conduit means providing communication between the upper portions of said chambers and second conduit means providing communication between the lower portions of said chambers, said reservoir and said hollow member being filled with at least two immiscible fluids having different specific gravi ties; said reservoir chamber being securely fastened to the drill string adjacent the drill bit and disposed to permit said hollow member to vibrate; means positioned adjacent to upper end of the drill string for detecting vibrations induced in the drill string by said hollow member; circuit means for determining the frequency of said induced vibrations.

4. An inclinometer for drill strings comprising: an enclosedreservoir chamber; a hollow vibrating member, said hollow member being connected to said reservoir chamber by two spaced tubular members; said reservoir and said hollow member being filled with at least two immiscible liquids having different specific gravities; said reservoir chamber being securely fastened to the drill string adjacent the drill bit and disposed to permit said hollow member to vibrate; means positioned adjacent the upper end of the drill string for detecting the vibrations in the drill string; filter means for removing all vibrations having frequencies substantially different from the frequency band of the vibrations induced in the drill string by said hollow member and circuit means for determining the value of said remaining vibrations.

5. An inclinometer for drill strings comprising: an enclosed reservoir chamber; a hollow vibrating member, said hollow member being connected to said reservoir chamber by two spaced elastic tubular members; said reservoir and said hollow member being filled with at least two immiscible liquids having different specific gravities; said reservoir chamber being securely fastened adjacent the lower end of the drill and disposed to permit said hollow member to vibrate; means positioned adjacent the upper end of the drill string for detecting the vibrations in the drill string and converting them to a fluctuating electrical signal having a frequency proportional to the frequency of said vibrations; circuit means for filter- T .ingsaid fluctuating signal to remove all frequencies subelastic means for connecting said reservoir and said vibrating chambers together, conduit means for providing fluid communication betweensaid chambers, said reservoir and said hollow member being filled; with at least two immiscible fluids having different specific gravities; said reservoir chamber being securely fastened to the drill string adjacent the drill bit and disposed to permit said hollow member to vibrate; and means for determining the frequency of vibration of said hollow member.

2. An inclinometer for drill strings comprising: an enclosed reservoir chamber; a hollow vibrating chamber,

stantiall'y different from those frequencies corresponding to the vibrations induced in the drill string by said hollow member and means for determining the frequency of the remaining frequencies.

References Cited in the tile of this patent UNITED STATES PATENTS France Apr. 18, 1908 

